An airplane passenger videoed a mysterious oval white object flying over Seoul, South Korea, on April 7. The video has been lighting up the Internet since, and of course many people are offering extraterrestrial explanations.

As is de rigueur these days, the UFO clip was uploaded to YouTube, where it has been viewed millions of times. Some comments say it's clearly an extraterrestrial spacecraft; others insist it's a fake. Still others say it's neither but instead is a real object — such as a plastic bag in the wind, a parachute seen from above, or a drop of water on the window — that simply looks strange from that angle.

Aside from the anonymity of the cameraman, the video raises some red flags about its authenticity. For one thing, the video is not complete; it has been purposely edited to leave some information out. We know this because it begins in progress, with the UFO already well in frame, in the lower right-hand corner. The video camera didn't suddenly turn on to capture that scene; there must be at least some video that was recorded the first few seconds of the camera being turned on or the cameraman pointing the camera out the window. This type of selective editing is common among UFO hoax videos.

There's also the fact that the cameraman waits almost seven seconds before he mentions the UFO to his companion. It's clearly present, and it would be hard to keep your reaction to yourself if you were watching while you were videotaping.

Perhaps most strange, even though he clearly spots the UFO, the cameraman makes no effort to follow the object after it zooms up and out of frame; instead he videotapes more or less the same area of sky for the remaining 10 seconds of the clip. [Video of UFOs Swarming Over Las Vegas Is for the Birds]

While these internal clues suggest something's not right with the video, the question remains: Was it a real object? Some of the most popular explanations don't fit the facts. A plastic bag, for example, would be unlikely to reach that altitude (and would not appear that large), and a parachute could not move as seen in the video.

The best earthly explanation for the UFO is that it's a droplet of water on the outside of the window being pushed up by airflow coming from under the fuselage. This would explain why the UFO is out of focus: because it's close to the lens. It would not, however, explain why the UFO appears to maintain a constant shape. Droplets of water, especially when subjected to high pressure, tend to deform and leave droplet trails as they move across a smooth surface. This one does not.

Then there's the fact that the light and shadow pattern on the blurry white object doesn't change as it moves. It's almost as if the UFO intentionally maintained exactly the same angle toward the camera the whole time — not impossible, but highly suspicious.

Absent a terrestrial explanation, we turned to Derek Serra, a Hollywood visual effects artist who has analyzed previous UFO videos. Serra said he finds several elements in this South Korean UFO video that "scream fake," including that "the motion blur was done by an amateur," he told Life's Little Mysteries.

"When the camera zooms in a bit, and when the UFO flies off screen, you can seen 'ghosting' of the image," Serra said. "Actual motion blur of real, three-dimensional objects creates a smooth gradient, not a stuttered ghosting like we see in this video. It is something we make sure we do right when working on shots for TV and film."

Though all signs point to a hoax, it's possible that alien spacecraft technology is so advanced that the spacecraft have the sneaky ability to appear on our cameras looking exactly like faked video images.

UFO investigators see references to rocket ships, aliens and astronauts that go back to the days when humans first put chisel and paintbrush to rock. More than 6,000 years later, objects that are unidentified — at least at first — continue to appear in the skies and generate buzz.

Take, for example, the blazing pinwheel that appeared in Norwegian skies in December 2009, shown here. The sight sparked speculation that aliens were sending earthlings a signal. Other researchers speculated — and the Russian military later confirmed — that a missile failed.

NBC space analyst James Oberg says the incident fits into a long tradition of UFO sightings over Russia that are caused by secret military and space activities. Even when there's a prosaic explanation for the sightings, they can provide useful information about covert activities.

Click onward to learn about seven more UFO cases through time that generated buzz.

— John Roach, msnbc.com contributor

1897: Did an airship crash in Aurora, Texas?

MUFON

In the 1800s, sightings of UFOs, called airships, streamed in from across the United States, according to Mark Easter, a field researcher and international director of public relations for the Mutual UFO Network, or MUFON. Many of these sightings were explained as hot-air balloons, which were becoming a fad then. A reported UFO crash in Aurora, Texas, however, remains inadequately explained, according to a report by the group.

Among the evidence recovered during MUFON's investigation is an unusual piece of metal with properties consistent with a crash landing, shown here in a black-and-white view from the report. What's more, remains of the alien pilot are said to be interred at the local cemetery. Requests to excavate the grave, however, have been denied. Why?

A local historian concluded that the sighting was a hoax meant to drum up interest in the town at a time it was being bypassed by the railroad. Excavating the grave might expose the hoax. Oberg, however, says that cases such as the Aurora crash are immune to disproof — too much time has passed to rely on stories that could would have mutated and been embellished over the years, and there's no remaining physical evidence to study.

On June 24, 1947, former World War II pilot Kenneth Arnold was flying near Mount Rainier in Washington state when he spotted a chain of nine crescent-shaped objects that he said skipped across the air like saucers. Newspaper reporters, erroneously, called them "flying saucers."

"The phrase 'flying saucers,' which are assumed to be round like a saucer, spread so quickly that people began seeing not what he saw but what the reporters had misdescribed," Oberg said. The technical description of whatever Arnold saw has rarely been reported again, the space analyst added.

Other researchers, according to MUFON's Easter, put the sighting in the historical context of the post-World War II atomic weapons program. This activity, he notes, could in theory attract extraterrestrial attention. Plutonium for the bombs was processed at the Hanford Nuclear Reservation east of Mount Rainier.

"If there's some surveillance going on, these things, whatever they were, it just makes sense they would be hugging the east side of that mountain when Arnold saw them," Easter said. Doing so, he noted, would have helped shield them from detection by radar.

1947: The Roswell incident

Justin Norton
/
AP

Did UFOs crash-land in the desert outside of Roswell, New Mexico, in July 1947? According to the official line from the U.S. military, the answer is no. At the time, fragments of strange debris collected by a local rancher were explained away as an experimental weather balloon gone awry. In 1994, the military changed its story, saying that the balloon was actually part of Project Mogul, a covert operation to monitor Soviet nuclear blasts.

Oberg is satisfied with that explanation, but some members of the UFO community view the military's explanation as a cover-up of another kind. MUFON's Easter, for example, lends credence to a theory that the military shot down two spaceships that were checking out nuclear weapons being developed and tested in New Mexico. One crash site was cleaned up before it leaked to the press; the other became known as the Roswell Incident.

Amid the buzz, one thing is certain: The mystery has generated income for merchants in Roswell who play up the incident, including this unquestionably fake alien on display at a local museum.

1952: UFO buzz hits Washington

Gail Shumway
/
Getty Images

By 1952, according to MUFON's Easter, UFO fever was at such a high pitch that sighting reports started to clog telephone networks. The buzz hit a crescendo during two consecutive July weekends with a series of visual and radar sightings over Washington, D.C.

The military explained the wave of sightings on a temperature inversion, which can cause interference with light and radar. Skeptical members of the UFO community, however, see the time frame as the beginnings of a government-orchestrated mission to squelch the UFO phenomenon by making fun of the people who reported the sightings.

Oberg says the government was concerned about the flood of calls - it was interfering with communications. Security experts reasoned that enemies could purposely spread UFO panic to tie up lines of communication as they dropped bombs on U.S. cities. Instead of debunking the UFOs - which was an option studied - the military shored up its communications systems.

Some UFO researchers say an inadequately explained sighting at a nuclear missile launch site near Malstrom Air Force Base, shown here, in March 1967 bolsters the case for a connection between nuclear weapons development and UFOs.

According to a MUFON investigation into the matter, retired Air Force Capt. Robert Salas, who was stationed at the site, said sightings of UFOs with pulsating red lights were followed by a rapid shutdown of the missiles' targeting system. The military admits the shutdown occurred, but its own investigation concluded that the UFO sighting was a rumor.

Oberg says he'd like to know more about the events surrounding this incident. He notes that the tale sounds similar to a case in Russia in which officials used UFOs as an excuse to explain why nuclear equipment was faulty.

1980: A diamond in the sky

BJ Booth
/
UFO Casebook

In December 1980, Betty Cash, Vickie Landrum and Vickie's grandson Colby were looking for a bingo game in Texas when a diamond-shaped UFO appeared in the sky. Moments later, the UFO seemed to be escorted away by a fleet of helicopters - some similar to a type used by the U.S. military, according to various accounts of the UFO incident known as the Cash-Landrum Case.

After the incident, Cash and the Landrums reported symptoms such as nausea and burns that some experts believe to be radiation poisoning. Cash spent more than two weeks in the hospital. The trio sued the U.S. government for compensation, but the case was dismissed because a government connection to the incident could not be shown and the medical condition of the alleged victims prior to the incident remained sealed under privacy protection laws.

"That was an interesting case in the sense that it was one of these outliers that have a bright light being carried away by helicopters low across the skies," Oberg says. "That's really bizarre and as far as we know, that, if accurately reported, was the only case where that ever really happened."

2008: Did fighter jets chase Texas UFOs?

NBC Nightly News

Dozens of people in rural Texas near Stephenville reported seeing a large object with bright lights flying low and fast in the skies on Jan. 8, 2008, apparently chased by F-16 fighter jets. At first, the Air Force denied they had jets in the area at the time. Two weeks later, the military admitted that there were indeed jets in the area, and suggested that the residents might have seen one of the jets as a UFO.

The admission satisfies some people as a reasonable explanation. Many such sightings turn out to be military operations. Others, however, remain unconvinced that the larger object has been adequately explained.

Oberg says even he has been fooled by jet overflights. When the line of jets passes overhead, the lights of the leading jet can be seen long before any sound arrives from it. By the time the second and third jets fly over, the roar is evident and it looks as if the jets are chasing the "silent" light out front. "I was shocked by just how gripping, how persuasive, the illusion was that the roaring jets were following a silent light in front," he says.

Southern stargazing

Stars, galaxies and nebulas dot the skies over the European Southern Observatory's La Silla Paranal Observatory in Chile, in a picture released on Jan. 7. This image also shows three of the four movable units that feed light into the Very Large Telescope Interferometer, the world's most advanced optical instrument. Combining to form one larger telescope, they are greater than the sum of their parts: They reveal details that would otherwise be visible only through a telescope as large as the distance between them.
(Y. Beletsky / ESO)
ShareBack to slideshow navigation

A balloon's view

Cameras captured the Grandville High School RoboDawgs' balloon floating through Earth's upper atmosphere during its ascent on Dec. 28, 2013. The Grandville RoboDawgs’ first winter balloon launch reached an estimated altitude of 130,000 feet, or about 25 miles, according to coaches Mike Evele and Doug Hepfer. It skyrocketed past the team’s previous 100,000-feet record set in June. The RoboDawgs started with just one robotics team in 1998, but they've grown to support more than 30 teams at public schools in Grandville, Mich.
(Kyle Moroney / AP)
ShareBack to slideshow navigation

Spacemen at work

Russian cosmonauts Oleg Kotov, right, and Sergey Ryazanskiy perform maintenance on the International Space Station on Jan. 27. During the six-hour, eight-minute spacewalk, Kotov and Ryazanskiy completed the installation of a pair of high-fidelity cameras that experienced connectivity issues during a Dec. 27 spacewalk. The cosmonauts also retrieved scientific gear outside the station's Russian segment.
(NASA)
ShareBack to slideshow navigation

Special delivery

The International Space Station's Canadian-built robotic arm moves toward Orbital Sciences Corp.'s Cygnus autonomous cargo craft as it approaches the station for a Jan. 12 delivery. The mountains below are the southwestern Alps.
(NASA)
ShareBack to slideshow navigation

Accidental art

A piece of art? A time-lapse photo? A flickering light show? At first glance, this image looks nothing like the images we're used to seeing from the Hubble Space Telescope. But it's a genuine Hubble frame that was released on Jan. 27. Hubble's team suspects that the telescope's Fine Guidance System locked onto a bad guide star, potentially a double star or binary. This caused an error in the tracking system, resulting in a remarkable picture of brightly colored stellar streaks. The prominent red streaks are from stars in the globular cluster NGC 288.
(NASA / ESA)
ShareBack to slideshow navigation

Supersonic test flight

A camera looking back over Virgin Galactic's SpaceShipTwo's fuselage shows the rocket burn with a Mojave Desert vista in the background during a test flight of the rocket plane on Jan. 10. Cameras were mounted on the exterior of SpaceShipTwo as well as its carrier airplane, WhiteKnightTwo, to monitor the rocket engine's performance. The test was aimed at setting the stage for honest-to-goodness flights into outer space later this year, and eventual commercial space tours.

Red lagoon

The VLT Survey Telescope at the European Southern Observatory's Paranal Observatory in Chile captured this richly detailed new image of the Lagoon Nebula, released on Jan. 22. This giant cloud of gas and dust is creating intensely bright young stars, and is home to young stellar clusters. This image is a tiny part of just one of 11 public surveys of the sky now in progress using ESO telescopes.
(ESO/VPHAS team)
ShareBack to slideshow navigation

Fire on the mountain

This image provided by NASA shows a satellite view of smoke from the Colby Fire, taken by the Multi-angle Imaging SpectroRadiometer aboard NASA's Terra spacecraft as it passed over Southern California on Jan. 16. The fire burned more than 1,863 acres and forced the evacuation of 3,700 people.
(NASA via AP)
ShareBack to slideshow navigation

Where stars are born

An image captured by NASA's Spitzer Space Telescope shows the Orion Nebula, an immense stellar nursery some 1,500 light-years away. This false-color infrared view, released on Jan. 15, spans about 40 light-years across the region. The brightest portion of the nebula is centered on Orion's young, massive, hot stars, known as the Trapezium Cluster. But Spitzer also can detect stars still in the process of formation, seen here in red hues.
(NASA / JPL-Caltech)
ShareBack to slideshow navigation

A long, long time ago...

This long-exposure picture from the Hubble Space Telescope, released Jan. 8, is the deepest image ever made of any cluster of galaxies. The cluster known as Abell 2744 appears in the foreground. It contains several hundred galaxies as they looked 3.5 billion years ago. Abell 2744 acts as a gravitational lens to warp space, brightening and magnifying images of nearly 3,000 distant background galaxies. The more distant galaxies appear as they did more than 12 billion years ago, not long after the Big Bang.
(NASA / NASA via AFP - Getty Images)
ShareBack to slideshow navigation

Frosty halo

Sun dogs are bright spots that appear in the sky around the sun when light is refracted through ice crystals in the atmosphere. These sun dogs appeared on Jan. 5 amid brutally cold temperatures along Highway 83, north of Bismarck, N.D. The temperature was about 22 degrees below zero Fahrenheit, with a 50-below-zero wind chill.